JPS5955310A - Regenerating method of permselective membrane - Google Patents

Abstract

PURPOSE:To restore easily the decreased performance of a permeable membrane by treating an org. material having a carboxylic group deposited strongly on a membrane surface with a neutral aq. soln. of alkali metals and/or alkaline earth metals. CONSTITUTION:Ethylenediamine modified polyepichlorohydrin and isophthaloyl chloride are crosslinked on a polysulfone ultrafilter membrane, whereby a flat film-like composite film is obtd. When such membrane is mounted in a flow type cell and the process liquid extract of a medical plant consisting essentially of org. materials having carboxylic groups is supplied to the cell continuously for 199hr under 40kg/cm<2> at an ordinary temp., the rate of permeation decreases from initial 0.67m<3>/m<2>.day to 0.38m<3>/m<2>.day. Thereupon, when a 2wt% aq. soln. of magnesium sulfate is circlated and supplied to the cell for one hour under the conditions of 30 deg.C and 5kg/cm<2> pressure, the rate of permeation is restored up to 97% of the initial rate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating a selectively permeable membrane, and more specifically, the present invention relates to a method for regenerating a selectively permeable membrane. The present invention relates to a method for regenerating a selectively permeable membrane by washing it to remove the above-mentioned organic substances and restoring its membrane performance.

In recent years, membrane treatment using selective permeable membranes such as reverse osmosis membranes and ultrafiltration membranes has been put into practical use in the treatment of industrial wastewater, separation and concentration processes in the production of foods, medicines, chemicals, etc. It has been reached. However, in such membrane treatment, components in the treatment stock solution, especially organic substances, gradually deposit on the membrane surface and contaminate the membrane, so that a decrease in membrane performance, especially water permeation rate, is unavoidable.

Therefore, various methods have been proposed in the past for cleaning the membrane surface on which organic substances have been deposited and restoring the membrane performance.

For example, methods using aqueous solutions of anionic and nonionic surfactants such as commercially available synthetic detergents, methods using aqueous solutions of enzymes such as protease and α-amylase, and methods using oxidizing agents such as hypochlorous acid and hydrogen peroxide. However, depending on the deposited substances, these methods have almost no removal effect from the membrane surface, or it takes an extremely long time to recover membrane performance, and furthermore, these methods may alter and deteriorate the membrane. There are also other problems. In particular, organic substances having carboxyl groups are particularly strongly deposited on the membrane surface due to the interaction between the carboxyl group and the membrane surface.

Therefore, it is difficult to effectively remove it using conventional cleaning methods.

The present inventors conducted extensive research to solve the above-mentioned problems, and found that a selectively permeable membrane, in which organic substances with carboxyl groups were deposited on the membrane surface and the membrane performance had deteriorated, was treated with a neutral inorganic salt aqueous solution. They discovered that by cleaning, the organic substances mentioned above can be removed in a short time and the membrane performance can be easily restored.
This led to the present invention.

The method for regenerating a selectively permeable membrane according to the present invention is to recover a selectively permeable membrane in which an organic substance having a carboxyl group has been deposited on the membrane surface.
It is characterized by treatment with an aqueous solution containing an alkali metal salt and/or an alkaline earth metal salt and having a pH of 6 to 8.

In the present invention, a selectively permeable membrane typically refers to a membrane that does not selectively permeate a specific solute component in a solution, such as a reverse osmosis membrane or an ultrafiltration membrane, and various types of membranes are already available. Are known. Specific examples include anisotropic polymers such as cellulose esters such as cellulose acetate, polyamides, polyimides, polyhenzimidazolone, polysulfones, polyethersulfones, sulfonated polysulfones, polyolefins, polyvinyl chloride, and polyacrylonitrile. Examples include membranes and composite membranes in which an ultra-thin membrane made of polyamide, polyurea, polyfuran, etc. is directly formed on a polysulfone ultrafiltration membrane.

In the present invention, the organic substance containing a carboxyl group is not limited to a single substance, and its molecular weight may range over a wide range, for example, from high molecular weight substances on the contrary to hundreds of low molecular weight compounds. . The fact that the membrane surface is contaminated with such an organic substance having a carboxyl group can be determined by, for example, surface analysis means such as infrared absorption spectroscopy. A typical example of an organic substance having a carboxyl group is a carboxylic acid, but in the present invention, the organic substance may have an amino group or the like in addition to a carboxyl group, such as an amino acid. Such organic substances are contained in large quantities in natural ingredients such as animal and plant ingredients, as well as in synthetic foods, medicines, and chemical products, and are also discharged in large quantities from their manufacturing processes. For example, medicinal herb extraction processes, fermentation processes, etc. contain large amounts of organic substances having carboxyl groups in process water and wastewater.

The alkali metal salts and alkaline earth metal salts used in the present invention are water-soluble neutral salts such as lithium, sodium, potassium, calcium, and magnesium whose aqueous solution has a pl+ of 6 to 8, sulfates, hydrogen halides, etc. acid salt,
Neutral salts such as phosphates are preferably used. Here, water-soluble means having a solubility in water of 1% by weight or more at room temperature. Therefore, preferably sulfates and hydrohalides are used. Preferred specific examples of the neutral salts include sulfates such as sodium sulfate, potassium sulfate, and magnesium sulfate; hydrohalides such as lithium chloride, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, and sodium bromide; Examples include phosphates such as sodium dihydrogen phosphate and potassium dihydrogen phosphate.

These inorganic salts are used to improve membrane materials, structure, and deposition so that when a selectively permeable membrane on which organic substances with carboxyl groups are deposited is treated with its aqueous solution, membrane performance, especially water permeation, is maximized. It is best to select it experimentally depending on the properties of the organic substance. Generally, neutral sulfates are preferred.

Further, the concentration of the above inorganic salt aqueous solution is usually 0.1 to 1
0% by weight, preferably 0.5-5% by weight.

The treatment of the membrane with an aqueous solution containing the above-mentioned inorganic salts is preferably carried out by circulating and supplying this aqueous solution to the membrane surface under pressure.

Although the treatment temperature is not particularly limited, it is usually 5~
The temperature is 80°C, preferably 20 to 50°C, and is selected to be below the heat resistance temperature of the target film. However, depending on the material of the film, it is of course possible to process at a high temperature exceeding the above range. The treatment time depends on the properties of the deposited organic matter, the type and concentration of the inorganic salt used, etc., but is generally about 10
The time may be from minutes to several days, preferably from 0.5 to 5 hours. Other methods of regeneration treatment include a method in which the membrane is immersed in an aqueous inorganic salt solution and a method in which the membrane is allowed to stand still, a method in which an aqueous solution is permeated under pressure, and the like.

What is the morphology of the membrane treated by the method of the present invention? = 1, but is not limited to the shape, and may be in any shape such as a flat plate, a tube, a spiral, a hollow fiber, etc. In addition, in order to enhance the cleaning and regeneration effect of the membrane, stirring 1. Physical cleaning such as friction and ultrasonic cleaning may also be used together.

According to the method of the present invention, a selectively permeable membrane in which an organic substance having a carboxyl group is deposited on the membrane surface and the membrane performance, particularly the water permeation rate has decreased, is removed from a neutral aqueous solution of an alkali metal and/or alkaline earth metal. By washing with water, the organic substance described in 1- is specifically removed from the membrane surface, and thus the membrane recovers almost its initial performance, and there is no fear of alteration or deterioration of the membrane. Although it is not necessarily clear why organic substances with carboxyl groups are specifically removed by treating the membrane with a neutral aqueous solution of inorganic salts, it is likely that the carboxyl groups interact with the membrane surface. organic substances are
It can be considered that when the membrane is treated with the above-mentioned inorganic salt aqueous solution, the inorganic salt acts more strongly on the metal ions7, and as a result, the deposited organic substances are easily removed from the membrane surface.

Although the present invention will be described above with reference to Examples, the present invention is not limited to these Examples in any way.

Example 1 According to the method described in Japanese Patent Publication No. 54-38164, ethylenediamine-modified polyepichlorohydrin and isophthalic chloride/t-1yl chloride were crosslinked on a polysulfone ultrafiltration membrane to form a flat membrane. A composite permeable membrane was obtained. This membrane was attached to a flow cell to create an experimental module.

The medicinal herb extraction process liquid, which is mainly composed of organic substances with carboxyl groups, is prepared at room temperature at 40 kg/en! 100 at a pressure of
When water was continuously supplied to the membrane module for hours, the water permeation amount was 0.67r+? /-・Day?

It decreased to 0.39 confidence/(・1).

Therefore, a 2% by weight aqueous solution of magnesium sulfate was added at a temperature of 30%.
When the membrane was circulated for 1 hour at a temperature of 5 kg/ctA and a pressure of 5 kg/ctA, the water permeation rate recovered to 0.65 m/m/day under the same conditions as above, a recovery rate of 97%.
).

Example 2 The membrane after continuous operation was treated in the same manner as in Example 1 except that sodium sulfate was used instead of magnesium sulfate, and the water permeability of the glands was 0.
It recovered to 63 communications/m day (recovery rate 94%).

Example 3 When amino acid-containing pharmaceutical process wastewater was continuously supplied to the same membrane module as in Example 1 at room temperature and pressure of 40 kg/cn+ for 100 hours, the amount of water permeation decreased from the initial 0°58 ra.
/ 0.29n from m day? /m day.

Therefore, when a 2% by weight aqueous solution of calcium chloride was circulated and supplied to the above membrane under the same conditions as in Example 1, the water permeation rate recovered to 0.59 m/n (day) (recovery rate 100%). ).

Example 4 Polyvinyl alcohol and ethylene diamine were cross-linked with trimesic acid chloride using polysulfone film prepared according to the method described in JP-A-57-27102+IJ to obtain a selective composite permeate film II. child.

In Example 1, the medicinal herb extraction process liquid was subjected to membrane treatment in exactly the same manner as in Example 1 except that the TE force was supplied to the membrane module at 20 kg/cJ, and the water permeation rate was 1.
7rr? /n(-5 to 0.4-6 rd/ni
・Decreased daily.

Example 1: This membrane was coated with a 2% aqueous solution of magnesium sulfate.
When treated in the same manner as above, the water permeability was 1.65 I/I.
・He recovered within days (97% recovery rate).

Example 5 In Example 4, the membrane was treated in exactly the same manner as in Example 4, except that sodium chloride was used instead of magnesium sulfate, and the water permeation amount was 1.53 n? /n(
・Recovery rate is 90%.

Comparative Example 1 In Example 1, 2% by weight of the anionic surfactant sodium dodecylhenzensulfonate was added to the membrane after continuous operation.
An aqueous solution was supplied in the same manner as in Example 1, but the amount of water permeation after treatment was 0.42 r&/m day, which was almost the same as before treatment.

Comparative Example 2 A membrane was treated in the same manner as in Example 4, except that a sodium hydroxide aqueous solution having a pH of 12 was used instead of the magnesium sulfate aqueous solution. The membrane after treatment is
The water permeation rate was 3.50 m/ml/day, which was actually higher than the initial value, and the removal rate decreased from the initial 98% to 70%, indicating that the membrane had deteriorated.

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Claims (3)

[Claims] (1) A selectively permeable membrane in which an organic substance having a carboxyl group is deposited on the membrane surface is treated with an aqueous solution of PL (6 to 8) containing an alkali metal salt and/or an alkaline earth metal salt. Method for regenerating selectively permeable membranes. (2) The method for regenerating a selectively permeable membrane according to claim 1, wherein the metal salt is a sulfate and/or a hydrohalide. (3) The method for regenerating a selectively permeable membrane according to claim 1 or 2, wherein the inorganic salt aqueous solution contains 0.1 to 10% by weight of inorganic salt.